Heat flow measurements are widely used in medicine, for diagnosing building walls, the agricultural soils and the like, as described in U.S. Pat. Nos. 4,274,475; 5,524,618; 5,803,915; 6,533,731 and 6,595,929. Such measurements are characterized by placing heat flow sensors on opposite surfaces of a wall or barrier. The steady heat flow through the barrier can thus be measured. Heat flux and temperature differences can be digitally determined and recorded.
The shortcoming of these measurements is the fact that it is not always possible to place heat flow sensors on both sides of a wall or barrier. For example, without performing a surgical procedure, it is not possible to place heat flow sensors inside a living body. Similarly, without digging, it is not possible to place a sensor into the ground.